A far cry from the super-charged racing cars of today, the racing vehicle is unusual for Bugattis of its time period, featuring an exceptionally large engine and rear wheels driven by chains.
It also has the distinguished history of having raced at both Le Mans and the Mont Ventoux Hill Climb and boasts previous owners including the Duke of Bavaria and Nigel Arnold-Forster.
The 1912 model, numbered 471, is one of only three remaining racers built by founder Ettore Bugatti after he established his first factory in 1910.
The auction will be held at the Reims-Gueux circuit, France on September 26. Other items up for auction include a Ferrari 330 GTS convertible from 1968, and a 1937 Mercedes Benz 540K Cab. C.
Earlier this year, a different Type 18 Bugatti from 1913 was sold by Bonhams for 2.4 million Euros.